Gro-Tsen
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Registered User
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Apr 15 |
accepted | An exercise about Tor |
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Apr 15 |
answered | An exercise about Tor |
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Apr 2 |
comment |
Looking for a copy of Leo Harrington’s unpublished notes on the first nonprojectible ordinal Just saw this. Thanks a lot to you and others who helped in finding these notes! |
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Mar 20 |
awarded | ● Necromancer |
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Mar 2 |
awarded | ● Nice Question |
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Feb 25 |
asked | Looking for a copy of Leo Harrington’s unpublished notes on the first nonprojectible ordinal |
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Jan 24 |
answered | cryptographic primitive process |
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Jan 21 |
comment |
Does the proof of GAGA use the axiom of choice? There are two different questions one could ask: one is whether Serre's proof of GAGA uses the axiom of Choice, another is whether one can find a metamathematical argument that GAGA must be provable without Choice (an argument similar to the well-known fact that "any arithmetical statement that is provable in ZFC is provable in ZF alone"). I'm pretty convinced the answer of the second question is "yes" (perhaps something like "encode the analytic sheaf as a real number $x$ and argue in $L[x]$ where Choice holds"). But then, that's not what you asked. |
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Jan 20 |
awarded | ● Commentator |
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Jan 20 |
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A question regarding Koepke' s Ordinal Computability in HOD I'm not sure I understand what the question is, but $0^\#$, if it exists, is a hereditarily ordinal-definable set of ordinals (indeed, a $\Pi_1$-definable set of integers) that isn't constructible (hence not ordinal machine computable). |
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Jan 16 |
awarded | ● Disciplined |
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Jan 15 |
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Is equality of terms for “real” numbers with roots, logarithm, exponential, sin, cos, and other trigonometric operations decidable with a Turing-machine? @Ben Crowell: The cited article by Richardon does give an explicit algorithm, and claims that it was implemented and is actually usable. |
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Jan 15 |
accepted | Is equality of terms for “real” numbers with roots, logarithm, exponential, sin, cos, and other trigonometric operations decidable with a Turing-machine? |
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Jan 15 |
awarded | ● Organizer |
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Jan 15 |
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Is equality of terms for “real” numbers with roots, logarithm, exponential, sin, cos, and other trigonometric operations decidable with a Turing-machine? Note: I added the "lo.logic" and "algorithms" tags to the question. |
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Jan 15 |
revised |
Is equality of terms for “real” numbers with roots, logarithm, exponential, sin, cos, and other trigonometric operations decidable with a Turing-machine? edited tags |
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Jan 15 |
answered | Is equality of terms for “real” numbers with roots, logarithm, exponential, sin, cos, and other trigonometric operations decidable with a Turing-machine? |
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Jan 14 |
answered | Examples of interesting false proofs |
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Jan 14 |
awarded | ● Critic |
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Jan 14 |
awarded | ● Nice Question |
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Jan 14 |
asked | Does Taranovsky’s system of ordinal notations make sense? |
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Dec 8 |
awarded | ● Teacher |
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Dec 8 |
answered | Proof strength of Calculus of (Inductive) Constructions |
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Dec 8 |
asked | Arithmetic strength of Peano + the Howard ordinal |
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Nov 25 |
comment |
Explicit equation of Dickson invariant / quasideterminant / special orthogonal group over the integers @Matthieu Romagny: The equations of $O_{2n}$ are "explicit enough" in the sense that I can easily write down equations for all $n$, whereas for $SO_{2n}$ I don't know how to do this. I agree that there's no "canonical" choice for deg (it's only well-defined modulo the equations of $O_{2n}$), but I'm not asking for something canonical, I'm asking for something explicit, e.g., I choose $n=10$, can you write down a polynomial in $400$ variables which represents deg? The best I was able to do with Sage was $n=2$ (which doesn't inspire an obvious generalization). |
